DE 699 08 918 T2 discloses an air dryer wherein the air dryer cartridge is housed in a housing of the air dryer. The housing of the air dryer is built with two housing parts, namely a base element and a top cover element. The top cover element is in a first approximation bell-shaped comprising a side wall in the shape of a hollow cylinder and a dome-shaped top cover wall. The base element is assembled with the top cover element. In the assembled state the base element and the top cover element define a housing with a closed inner chamber being cylindrical with a dome-shaped arching at the top. The air dryer cartridge is located in the inner chamber. The air dryer cartridge comprises a housing which is generally closed but comprises passages, openings or ports for building inlets and outlets for the stream of pressurized air. The air dryer cartridge is housed with a minimal resulting radial gap with respect to the hollow cylindrical side wall of the top cover element. In a radial outer edge region a ring-shaped sealing element is interposed between the top wall of the top cover element of the air dryer and the air dryer cartridge. The sealing element comprises an oversize such that the cartridge and the sealing element are clamped between the base element and the top cover element for fixing the air dryer cartridge.
An air dryer cartridge according to DE 699 08 918 T2 builds two chambers, wherein one chamber is located radially inside from the other chamber. In the radial outer hollow cylindrical ring chamber, a desiccant and/or a filter is/are located. The outer chamber is separated by a hollow cylindrical intermediate wall from a radial inner cylindrical chamber wherein (another) desiccant is housed. During a load phase of the air dryer, pressurized air streams from an inlet chamber of the base element through passages of a base wall of the air dryer cartridge into the ring chamber. Within the ring chamber, the pressurized air streams parallel to a longitudinal axis of the air dryer cartridge to the top cover region of the air dryer cartridge. In the top cover region of the air dryer cartridge the pressurized air is transferred via an air-permeable textile material and an air-permeable top wall of the air dryer cartridge into an intermediate chamber. The intermediate chamber is build between the top wall of the air dryer cartridge and the top wall of the top cover element of the air dryer. The pressurized air streams from the intermediate chamber through the air-permeable top wall of the air dryer cartridge and through the air-permeable textile material into the radial inner cylindrical chamber. In this chamber the air streams with an orientation parallel to the longitudinal axis towards the base element. The pressurized air is then fed by air passages in the base region of the air dryer cartridge and an outlet chamber of the base element to the pressurized air system, in particular to the consumer circuits. Collected humidity and/or impurities are removed from the desiccant, the filters and the collecting chambers by use of reversed cleaned pressurized air in a regeneration phase of the air dryer cartridge.
In order to fix the particles of the desiccant in the chambers, in order to compact the desiccant and/or in order to apply a pressing force to the desiccant, the air dryer cartridge of DE 699 08 918 T2 comprises separate pressing elements for each chambers. The pressing elements are (similar to pistons) axially displaceable in the chamber. On the side opposite to the desiccant the pressing elements are supported by springs. These springs bias the pressing element and the desiccant with a predefined pressing force. One base of the springs is supported at the pressing element, whereas the other base of the springs is supported by a supporting element. According to DE 699 08 918 T2, this supporting element is built by a fixed base wall of the air dryer cartridge.
Air dryer cartridges with a supporting element for supporting a spring biasing the desiccant are also known from U.S. Pat. No. 4,673,419 A, U.S. Pat. No. 5,002,593 A and EP 0 137 909 B1. For these embodiments the supporting element is built by a top cover element building a fixed part of the housing.
Furthermore, so-called spin-on-cartridges are known. These types of cartridges are not clamped by a spring element between a base element and a top cover element of the air dryer. Instead, for these embodiments the air dryer cartridges comprise a solid and massy base wall with a central bore having an inner thread. The base wall is with its inner thread screwed on a connecting socket of the base element of the air dryer. The connecting socket at the same time serves as an inlet and/or outlet port for pressurized air to and/or from the air dryer cartridge.